In a hard or floppy disk drive system, a read/write head is moved across a data storage disk so as to be positioned over a selected one of the large number of substantially circular, concentric tracks in which data is recorded and/or reproduced The head is mounted on an actuator carriage so as to be positioned at the desired track. The actuator carriage may either move linearly along a radius of the disk to position the head, or it may be adapted for rotary travel around an axis to move the head radially across the disk surface from the innermost track to the outermost track.
In most hard disk drive systems, a plurality of disks are stacked on a spindle and a corresponding plurality of magnetic heads are used to read and/or write on respective surfaces of the disks. The magnetic heads "fly" over the surfaces of the disks on an air cushion generated by the rapid rotation of the disks themselves. When power is turned off, the actuator carriage is driven to move the magnetic heads to an information-free parking or landing zone on which they may rest without destroying information, which is recorded only in other areas of the disks. Typically, the actuator carriage brings the heads quickly to the parking zone in case of error or loss of power, and generally a crash stop is provided to limit further movement of the actuator carriage once it reaches its stop position in the parking zone. The crash stop is conventionally in the form of a pin which may or may not be preloaded. Given the relatively small sizes of disk drives, for example to read and write on a 31/2 inch disk, it is a significant part of the design of the disk drive to precisely position the actuator carriage at its stop position so as to minimize the area of the information-free parking zone, which is essentially wasted disk surface space since no information can be recorded therein, while being certain that the heads will not be moved too far and off the surface of the disk.
Once the actuator carriage has been moved to its rest position abuting the crash stop, it is frequently desirable to latch the actuator carriage, for example when the disk drive is being moved, so that the heads will not move from the parking zone. The latch itself has to fit and function within the strict design tolerances for the disk drive system. It must also be surely moved between its free position, at which the actuator carriage is free to move the heads across the surface of the disk, and its latched position, at which the actuator carriage is held at its stop position. While it is known to use a solenoid to move the latch back and forth between the free and latched positions, it is undesirable to use the solenoid to actively hold the latch at either position, since this would require a constant current and therefore a constant drain on a battery or other power source. Instead, it is preferable to actuate the solenoid merely to move the latch between the two positions. However, the actuator carriage is heavy relative to the latch and will therefore exert some force on the latch when the disk drive is tilted or shaken during movement. Some conventional disk drive systems have therefore actively held the latch against the actuator carriage to latch the actuator, or have actively held the latch in the free position and used a spring to force the latch to the latched position and hold it there against the actuator.